Induction terminal unit for air-conditioning systems

ABSTRACT

The present invention provides a new type of induction terminal unit in which a pure fluid system is used to control the switching of the air between the conditioning and nonconditioning paths of the unit. The fluidic control system permits a simplification in the construction of the unit as well as a more efficient and effective operation of it.

[ Oct. 15, 1974 INDUCTION TERMINAL UNIT FOR AIR-CONDITIONING SYSTEMS 3,275,014 9/1966 Plasko 165/35 [75] Inventor: Gene W. Osheroff, Las Vegas, Nev.

- Primary ExammerCharles Sukalo [73] Assignee: Fluidtech Corporation, Inglewood, Attorney, Agent, or FirmAllen E. Botney Calif.

[22] Filed: Feb. 20, 1973 [21] Appl. No.: 334,124 [57] ABSTRACT Related U.S. Application Data 62] Division f 158,766111), 1, The present invention provides a new type of induction terminal unit in which a pure fluid system is used 52] U.S. c1 165/22, 165/39, 165/123 to control the Switching Of the air between the cohdh 51 1m. (:1 F24f 3/00 honing and non-conditioning Paths of h unit. The [58] Field of Search 137/815; 165/123, 222, fluidic control System Permits Simplification in the 165/35 2 39 40 construction of the unit as well as a more efficient and effective operation of it. [56] References Cited UNITED STATES PATENTS 14 Claims, 8 Drawing Figures 3,217,788 11/1965 Adam 165/123 l \ll'llilll l6: 18 FLUwlC/i BYPASS PLENUM l CONTROL 9 5 O l STEM COIL PLENUM unnno L J F Zxlttnurf Hume BYPASS: PLENUM --l CONTROL 9 gym-Ml, con. PLENUM 1 f I R l 1111111111 1 PAIENIEDacI 1 sum sum 10F 1 llllllll IIJ lllllll IIIJ x fi i Ti 3 lu \II l\ Tr. 4f Iv 4 1: M M 1 n M .N la U MI m u m N Q m fig hi IL! S D. A1. I! D- ll m m w c m 2M w m; H h m? L, um mum mmn DR w u 5 mfi w n Y R I. R

INDUCTION TERMINAL UNIT FOR AIR-CONDITIONING SYSTEMS This application is a division of the prior application filed July l, 1971, and having Ser. No. l58,766.

The present invention relates to air-conditioning systems in general and more particularly relates to an improved induction-type terminal unit for airconditioning systems.

In any air-conditioning system employing terminal units, the terminal unit is the mechanism or the device through and by means of which the hot or cold air is fed into the room or zone to be conditioned. Terminal units are very widely used and there are a number of different kinds. One such device is known as an induction terminal unit and it is called this because a major portion of the conditioned air fed into the room or zone to be conditioned is ambient air that has been sucked or induced into the terminal unit where it is either cooled or heated before being returned to the room or zone.

More particularly, in the standard or usual induction terminal unit found in the prior art, cold or hot air, depending on whether the room or zone to be conditioned is to be cooled or heated, is ducted at a relatively high velocity to and through the unit into the room or zone. Because of its velocity, the already conditioned air creates a partial vacuum or, stated differently, it produces a zone of reduced pressure in the unit, with the result that ambient air is pulled or induced into the unit. Furthermore, the terminal unit is so designed that the ambient air entering it is forced to pass over a coil through which either cold or hot water is circulated, depending, of course, on whether the room or zone to be conditioned is to be cooled or heated. By so doing, the ambient air is either cooled or heated, after which it mixes with the high velocity ducted air and passes into the room or zone with it. In the event the room or zone is at the desired temperature and, therefore, requires no conditioning, a baffle in the terminal unit is opened, thereby providing a second path for the ambient air that bypasses the coil. Thus, with the baffle open, the ambient air is not cooled or heated before it mixes with the relatively small percent of ducted conditioned air, with the result that the room or zone is now no longer supposed to be conditioned.

One of the disadvantages, however, of these prior art induction terminal units is that the baffle doesnt fully open so that instead of providing a low impedance bypass path for the ambient air, the baffle, in fact, continues to present a significant impedance. Consequently, as between the two paths available to the ambient air, namely, the path through the coil and the bypass path provided by the baffle, a significant portion of the ambient air continues to flow past the coil and thereby continues to be cooled or heated, which means that the room or zone continues to be conditioned. Thus, the baffle is not an effective means for turning the airconditioning off. Added to this is the further disadvantage that a relatively complex mechanical linkage and valve arrangement that is sensitive to both room temperature and line pressure is used in these units to open and close the baffle as conditions warrant. Needless to say, such an arrangement is not only cumbersome, but also adds considerably to the manufacturing and maintenance costs. Other disadvantages can be mentioned, but enough has been said to clearly point out that there has been a long-felt need for improvements in this par ticular art.

The present invention overcomes the abovementioned and other disadvantages of the induction terminal units found in the prior art and it does so by replacing the mechanical linkage and valve arrange ment with a pure fluid control system for switching the ambient air between the two paths. The introduction of a pure fluid control system makes still other improvements possible in the construction of the terminal unit, such as, for example, the elimination of the baffle and the almost complete isolation of the bypass path from the path through the coil. Since pure fluid devices do not involve any moving parts and because of the greatly simplified construction of these units, it will be recognized by those skilled in the art that the present invention greatly reduces the manufacturing and/or maintenance costs of this type unit. A further advantage that needs to be mentioned is that a fluidic control system acts or operates faster than the mechanical control systems previously used, with the result that induction terminal units according to the present invention react or respond more rapidly to changing environmental conditions.

Itis, therefore, an object of the present invention to provide a fluidically-controlled induction terminal unit.

It is another object of the present invention to provide an induction terminal unit in which the bypass path is substantially isolated from the rest of the unit.

It is a further object of the present invention to provide an induction-type air-conditioning terminal unit that responds more rapidly to changes in environmental conditions.

It is an additional object of the present invention to provide a pure fluid technique for switching the flow of ambient air in induction-type terminal units.

It is still another object of the present invention to provide an induction-type air-conditioning terminal unit that requires far less maintenance during its lifetime.

It is a further and additional object of the present invention to provide an induction-type air-conditioning terminal unit that is materially more efficient and effective in its operation than heretofore possible.

The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation together with further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawings in which embodiments of the invention are illustrated by way of example. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention.

FIG. 1 is a block diagram of an air-conditioning system illustrating the basic features and principles of an induction terminal unit according to the present invention;

FIG. 2 is a perspective view illustrating the basic construction of one embodiment of an induction-type airconditioning terminal unit according to the present invention;

FIG. 3 is a side view of the FIG. 2 embodiment;

FIG. 4 is a schematic diagram illustrating one arrangement of a fluidic control system that may be used in an induction terminal unit according to the present invention;

FIG. 5 is a schematic diagram illustrating another arrangement of a fluidic control system that may be used in an induction terminal unit according to the present invention;

FIG. 5(a) is a schematic diagram of the thermostatic apparatus used in the FIG. 5 system showing the thermostatic valves in one extreme condition, namely, one in which one of the valves is closed and the other fully open; I

FIG. 5(b) is a schematic diagram of the same thermostatic apparatus showing the thermostatic valves in another extreme condition, namely, one in which the other of the valves is closed and the first valve fully open; and

FIG. 6 is a side view of another embodiment of an induction terminal unit according to the present invention in which twin coils are used, the figure also including a schematic diagram of one type of fluidic apparatus that may be used to control the operation of this embodiment.

For a consideration of the invention in detail, reference is now made to the drawings and particularly to FIG. 1 therein wherein a basic block diagram of an airconditioning system that incorporates a terminal unit according to the present invention is illustrated. The air-conditioning system services a plurality of rooms or zones, but only the first and the last of these rooms or zones, respectively designated R and R are shown in the figure.

Each room or zone has mounted within it, or coupled to it, an induction terminal unit generally designated 10, each such terminal unit, in turn, basically comprising a coil plenum 11 and a bypass plenum 12. Both plenums include means by which ambient air can enter or flow into them, such as a screen or grill of some sort, the means associated with coil plenum 11 being indicated or represented by the arrows designated 13 and the means associated with bypass plenum 12 being indicated or represented by the arrows designated 14. Arrows 13 and 14 may, when necessary, also indicate or represent the flow of ambient air into the respective plenums. The outputs of plenums 11 and 12 are respectively designated 15 and 16.

Finally, although now shown in this figure, each coil plenum also has a coil mounted therein in such a location and manner that any ambient air flowing into the plenum must first pass through or over the coil, thereby becoming heated or cooled depending, respectively, on whether the coil is a heating coil or a cooling coil. A cooling coil is one through which a coolant flows, such as cold water, while a heating coil, for example, is one in which hot water flows. As is well known by those skilled in the air-conditioning and related arts, it is a simple matter and a common practice to selectively feed either hot or cold water into these coils, for example, hot water when the weather is cold and cold water when the weather is hot. In this way, as will be seen, these terminal units can be used to condition a room or zone in all kinds of weather.

Coupled or linked to each terminal unit 10 is a fluidic control system 17 which, as its name implies, comprises one or more fluidic or pure fluid amplifier devices arranged and adapted to control the operation of the terminal unit in response to the action of a thermovalve therein. Each fluidic control system has an input channel 18 by means of which already conditioned air, either hot or cold, is fed into it and a pair of output or outlet channels 19 and 20 by means of which this previously conditioned air is directed to one or the other of the plenums, as determined by the aforementioned thermovalve. As shown in the figure, outlet channel 19 is coupled to coil plenum 11 and outlet channel 20 is coupled to bypass plenum 12. The construction of such terminal units and fluidic control systems are described in still greater detail below.

Completing the air-conditioning system illustrated in FIG. 1 is a system fan 21 that provides air under pressure to the system, a supply duct 22 by means of which air supplied by the fan is directed to the proximity of the rooms or zones to be conditioned, and apparatus 23 by means of which the air entering the supply duct is either heated or cooled depending on whether the system is, at the time, a heating or cooling system. As shown in the figure, supply duct 22 ultimately leads to input channels 18 of the fluidic control systems.

In operation, conditioned air at a relatively high velocity is supplied by the system to duct 22 and from there it flows into fluidic control systems 17 via their respective input channels 18. Depending on the particular type of fluidic control systems used and the respective settings of the thermovalves therein, the conditioned air may or may not be directed to coil plenum 11 in each room or zone. For sake of clarity and also to expedite the discussion, it would be well now to contime any further explanation of the operation to only one of the rooms or zones, such as R,, but it must be recognized beforehand that since the equipment in room or zone R is the same as the equipment in all the other rooms or zones, the explanation as to one is equally applicable as to all.

With the above in mind, it will be assumed that the conditioned air in fluidic control system 17 flows through its outlet channel 19 to coil plenum 11. This pre-conditioned air flows through coil plenum 11 at a relatively high velocity and then into room or zone R as indicated by arrow 15. However, because of the velocity of the air, a low pressure area is created or produced in the plenum, what may be termed a partial vacuum, that induces ambient air in the room or zone to flow into coil plenum 11, as indicated by arrows 13. In so doing, the ambient air passes over the cooling coil in the plenum and is thereby cooled before it mixes with the pre-conditioned air already therein. It is this mixture of pre-conditioned air and coil-cooled ambient air that then enters and cools the room or zone. On the other hand, if the pre-conditioned air flowing in fluidic control system 17 exits via outlet channel 20, it enters bypass plenum 12 instead where, as before, it flows at I stance, however, since there is no coil located in bypass plenum 12, the ambient air is not cooled at all before it mixes with the aforesaid pre-conditioned air but, rather, remains at room temperature. Since in these induction terminal units, the pre-conditioned air constitutes only a relatively small percent of the total air mixture, for example about 25 percent, it can be seen that when the ambient air is not cooled, such as when it passes through bypass plenum 12, the temperature of the total air mixture is then such that it will not cool the room or zone to any practical extent.

Although the operation was described hereinabove in connection with the flow of cold air in the system, it will be recognized that the operation is exactly the same with the flow of hot air except that the ambient air is then heated rather than cooled when it enters coil plenum 11.

A more detailed view of the constructional features of induction terminal unit in FIG. 1 is illustrated in FIGS. 2 and 3 to which attention is now directed. Coil and bypass plenums 11 and 12, respectively, are generally designated in FIGS. 2 and 3 which clearly show that each of these plenums is, in turn, made up of a couple of plenums. More particularly, coil plenum 11 includes a first plenum 11a, a second plenum 11b that is positioned above plenum 11a and spaced from it, and a plurality of air tubes or pipes 110 that interconnect plenums 11a and 11b. Plenum 11a is completely enclosed except for its near or input end which is open, whereas plenum 11b is completely enclosed except that its top and outside walls are made of a suitable screen, mesh or grill arrangement that permits air to enter and leave the plenum. The open end of plenum 11a is designated 11d, the top wall of plenum 11b is designated 112 and the outside wall of plenum 11b is designated 11f. As for air tubes 11c, while there may be as many as twenty such tubes utilized, it will be recognized by those skilled in the art that the actual number depends upon the size of the terminal unit, the quantity of air moving through the unit, the air pressure available, the diameter of the tubes, the allowable noise, and possibly still other factors.

Referring now to bypass plenum 12, this plenum also includes a first plenum 12a, a second plenum 12b positioned directly above plenum 12a, the two plenums having a common wall therebetween, and a plurality of air tubes or pipes 12c that interconnect plenums 12a and 12b. Plenum 12a is adjacent and parallel to plenum 11a and, like plenum 11a, plenum 12a is completely enclosed except for its near or input end which is open and designated 12a. Plenum 12b is also adjacent plenum llb but is L-shaped with the base portion of the L protruding between plenums 11a and 11b and constituting the above-mentioned space between them. As with plenum 11b, plenum 12b is completely enclosed except that its top and outside walls are fabricated of a suitable screen, mesh or grill arrangement that permits air to enter and leave it. As may be seen from FIGS. 2 and 3, this outside wall of plenum 12b lies between the outside walls of plenums 11a and 11b. The top wall of plenum 12b is designated He and its referred-to outside wall is designated 12f.

Finally. completing the construction of terminal unit 10 is a coil 24 of the type through which hot or cold water can be circulated. Coil 24 is mounted in plenum llb immediately behind outside wall 11f so that ambient air passing through the wall comes into contact with the coil to be either heated or cooled by it, as previ ously mentioned. The actual means by which the water (or other fluid) is fed to the coil does not form a part of this invention and, furthermore, has been very well known in the prior art for a long time. Accordingly, no

description of any such means is deemed necessary here.

The entire unit as described above is enclosed or housed in a suitable cabinet in which provisions are made to permit the ambient air to pass through to the unit inside.

In its operation, when pre-conditioned air enters plenum 110, it is forced by the air pressure therein to flow through tubes 11c into plenum 11b where it rises at a relatively high velocity until it ultimately passes through plenum wall 112 into the room or zone being conditioned. As was previously mentioned, because of the high velocity with which this pre-conditioned air moves, a low pressure region is created in plenum 1117 which, in turn, causes ambient air, that is to say, air in the room or zone, to flow toward and into this low pressure region. In so doing, this ambient air is brought into contact with coil 24 which either heats or cools it before it mixes with the pre-conditioned air already in the plenum. The mixture then moves together through the plenum and into the room or zone. Needless to say, if the pre-conditioned air is hot air, then the coil will heat the ambient air and if the pre-conditioned air is cold air, then the coil will cool the ambient air.

This flow of pre-conditioned air into plenum 11a and from thence through plenum 11b continues until the room or zone is conditioned to the desired extent, at which time the pre-conditioned air is switched by the fluidic control system to plenum 12a. When this is done, the preconditioned air is then forced through tubes into plenum 12b where a low pressure region is again created. As a result, the ambient air now passes through wall 12f and into plenum 12b instead of into plenum 11b, thereby bypassing coil 24. In this instance, therefore, the ambient air is not conditioned before it mixes with the pre-conditioned air already in plenum 12b. Since, as was previously mentioned, the preconditioned air constitutes only a relatively small percent of the overall mixture and the ambient air a major portion of it, the temperature of the air in the room or zone is now no longer being affected to any practical extent by the air coming through wall l2e. The ambient air continues to take this bypass path so long as the preconditioned air is directed into plenum 12a and this will be done until the room or zone needs to be conditioned again, at which time the flow of the pre-conditioned air will again be switched to plenum 1 1a by the fluidic control system.

One type of fluidic control system is schematically illustrated in FIG. 4 and it includes a bistable fluid amplifier device 25, a thermostat 26 and a pair of thermostatically controlled solenoids 27a and 27b that are mounted or coupled to the fluid amplifier device itself. As will be seen below and understood by those skilled in the art, the thermostat and the solenoids together form a thermovalve that controls the operation of the fluid amplifier. As for bistable fluid amplifier device 25, such devices, which are well known, include an inlet channel 25a through which the stream of pre-' 25a connects with supply duct 22, outlet channel 25b connects with plenum 12a, as is indicated by the output arrow designated 12a, and outlet channel 250 connects with plenum 11a, as is indicated by the output arrow designated 11a. Solenoids 27a and 27b are respectively mounted over the openings leading into control channels 25d and 25e and, as shown in the figure, they are also connected to thermostat 26.

In operation, it will initially be assumed that the temperature in the room or zone is such that the thermostat causes solenoid 27b to be activated so as to close the opening or entrance to control channel 252. As a result, the pre-conditioned air entering inlet channel 25a and passing through the device is directed to outlet channel 250 which, as was previously explained, feeds the preconditioned air into plenum 11a in the terminal unit. If the pre-conditioned air is cold air, the amplifier device will be triggered into this state when the thermostat is set at a temperature that is lower than the temperature in the room or zone. On the other hand, if the preconditioned air is hot air, the amplifier device will be triggered into this state when the thermostat is set at a temperature that is higher than the ambient temperature.

Since amplifier device 25 is of the bistable kind, the stream of pre-conditioned air will continue to flow to outlet channel 250 and from there to plenum 11a until the temperature in the room or zone being conditioned reaches the temperature at which the thermostat is set. At this point, thermostat 26 causes solenoid 27b to be de-activated and solenoid 27a to be activated instead, which means, respectively, that the entrance to control channel 25e is now open once again and the entrance to control channel 25d closed. When this occurs, the stream of pre-conditioned air is switched from outlet channel 25c to outlet channel 25b and, therefore, from plenum 11a to plenum 12a. The conditioned air will continue to flow to outlet channel 25b until the relative temperature conditions are once again such as to switch it back again to outlet channel 25c, thereby completing the cycle.

Another type of fluidic control system that can be used with induction terminal units of the present invention and which has an entirely different effect on them is shown in FIG. 5. More particularly, in this system, two fluidic amplifiers and a thermovalve are arranged to form an oscillator that alternately applies pulses of conditioned air to plenums 11a and 12a, first to plenum 11a and then to plenum 12a, the length or duration of the respective pulses at any one time being determined by the condition of the thermovalve at that time. Stated differently, depending on whether the temperature in the room or zone to be conditioned is above or below the temperature setting of the thermovalve and how far above or below, the pulses of conditioned air applied to plenums 11a and 12a may be of equal duration, that is to say, the air is divided equally between them, the duration of the pulses delivered to plenum 11a may be longer than those delivered to plenum 12a, or the duration of the pulses delivered to plenum 110 may be less than those delivered to plenum 12a. In any event, the pulses may or may not be of equal duration depending on temperature conditions.

In the fluidic control system illustrated in FIG. 5, the fluidic amplifiers are both of the bistable type, one being generally designated 28 and the other being generally designated 29. Amplifier 28 includes an inlet channel 28a through which the stream of conditioned air flows from the air-conditioning systems supply duct, a pair of outlet channels respectively designated 28b and 280 by means of which the conditioned air that enters inlet channel 28a selectively flows either to plenum lla or to plenum 12a, a pair of control channels respectively designated 28d and 28e by means of which the abovesaid stream of air can be controlled so as to selectively direct the air to one or the other of the outlet channels, and a chamber 28f located between the inlet and outlet channels and through which the stream of air must pass in going from the inlet channel to the outlet channels. In the embodiment shown, control channels 28d and 28e respectively lead to opposite sides of chamber 28f in order to exercise the desired control over the air flow, as is well known and understood by those skilled in the art and as will more clearly appear later.

Fluidic amplifier 29 is coupled between the inlet and outlet channels of amplifier 28 as well as to its control channels, and, like amplifier 28, include an inlet channel 290, a pair of outlet channels 29b and 290, and a pair of control channels 29d and 29e. It also includes a chamber between its input and output channels but because the second amplifier is schematically illustrated, the chamber here cannot be presented. Suffice it to say, therefore, that control channels 29d and 29e are likewise coupled to opposite sides of this chamber in order to exercise the control on the air flowing through this second amplifier necessary to direct the flow to one or the other of its outlet channels 29b and 290. As shown in the figure, inlet channel 29a is coupled to inlet channel 28a so that a small percentage of the air entering inlet channel 28a is tapped off and enters inlet channel 29a. As is also shown, outlet channels 29b and 290 respectively connect to control channels 28d and 282, with the result that air entering one or the other of outlet channels 29b and 29c will flow into and ultimately through its associated control channel to chamber 28f.

Finally, the FIG. 5 system includes a pair of Pitot tubes 30a and 30b respectively mounted in outlet channels 28b and 280 and, as shown by the broken lines in the figure, these Pitot tubes are respectively connected to control channels 28e and 29d. These Pitot tubes are also respectively connected or coupled to a pair of thermostatically-controlled air escape valves 31a and 31b, the thermovalve as a whole being designated 31. The thermovalve, which is located in the room or zone to be conditioned includes the well known bi-metallic coiled strip 31c which moves in a clockwise or counterclockwise direction according to temperature conditions. In addition to the above, the thermovalve also includes a pair of leaf or cantilever type spring members 31d and 3le on which are respectively mounted a pair of stops or elements 31 f and 31g by means of which the valves 31a and 31b are closed and opened. As can be seen from the figure, members 31d and 312 are attached or affixed at one of their ends to the free end of bi-metallic strip 31d, the stops or elements 31 f and 31g being mounted intermediate the ends of these cantilevered members and in alignment with valves 31a and 31b. In this kind of thermovalve apparatus, one or the other of escape valves 31a and 31b is closed or open depending upon the position of bi-metallic strip 310, but in no event will both of them be open simultaneously. However, both may be closed simultaneously.

Further details concerning the construction and operation of thermovalve 31 will be provided as needed hereinbelow in connection with the described operation of the FIG. fluidic control system.

Considering now the operation of this fluidic control system, it will be assumed with respect to amplifier 28 that outlet channel 28b leads to plenum 12a, as indicated by the arrow marked 12a, that outlet channel 280 leads to plenum 11a, as indicated by the arrow marked 11a, and that the conditioned air flowing through the device is initially exiting through outlet channel 280 and, therefore, going to plenum 11a. It is also initially assumed, therefore, that the conditioned air flowing through amplifier 29 is exiting through outlet channel 2% and from this outlet channel to control channel 28d. Finally, it will be initially assumed that the temperature in the room or the zone to be conditioned is such that in the thermovalve located therein, namely, thermovalve 31, bi-metallic strip 310 is in its center position, that is to say, in the position shown in FIG. 5, with the result that valves 31a and 3112 are both fully closed. Needless to say, bi-metallic strip 31c is in said center position and valves 31a and 31b are both closed when the temperature at which the thermovalve is set is substantially the same as the ambient temperature of the air in the room or zone in which the terminal unit is located.

Accordingly, with these assumptions in mind, a small portion of the air flowing in outlet channel 280 is picked up by Pitot tube 30b wherein it then travels both to control channel 29d and to valve 31b. Since, as previously assumed, valve 31b is closed, this air that is fed back to it cannot escape and it therefore enters control channel 29d wherein the full force thereof is applied to the stream flowing through the chamber of fluid amplifier 29. As a result and in accordance with well known and established fluidic principles, the direction of this second stream of air is switched from outlet channel 29b to outlet channel 290. When this happens, this second stream of air is then directed through control channel 28e against the main stream flowing through chamber 28f and this, in turn, causes the main stream to switch its flow from outlet channel 28c to outlet channel 28b. The pre-conditioned air is now going to plenum 12a.

However, it will be recognized that just as soon as the air begins to flow in outlet channel 28b, Pitot tube 30a picks up a small portion of this air and channels it back both to control channel 29e and to valve 31a. Since valve 31a is also completely closed, the air thusly sent back likewise cannot escape through valve 31a and,

therefore, the air ends up entering control channel 2% wherein the full force thereof is once again applied to the stream flowing through fluidic amplifier 29 to switch it from outlet channel 290 back to outlet channel 29b'. When this occurs, this second stream of air is once again directed through control channel 28d to chamber 28f, thereby causing the main air stream to return to its initially assumed flow pattern, namely, to outlet channel 280.

The cycle of operation described above repeats itself over and over again so long as thermovalve strip 310 is centered and both valves thereby closed. In short, the two fluidic devices and the thermovalve cooperate to produce a pulsed oscillation in which the main air stream switches back and forth equally between outlet channels 28b and 28c and, therefore, equally between plenums 11a and 12a. Thus, under the conditions just described, namely, where both valves 31a and 31b are closed, the pulses are of equal duration.

For a further understanding of the operation of this fluidic control system, assume now that bi-metallic strip 31c is in its extreme counterclockwise position, as is illustrated in FIG. 5(a). In this position of strip 310, valve 31a is closed and valve 31b is totally open. As before, it will also be assumed that the conditioned air is initially exiting through outlet channel 280 to plenum lllla. Accordingly, a small portion of the air flowing in outlet channel 28c is picked up by Pitot tube 30b and fed back by it both to control channel 29d and valve 31b. However, since valve 31b is completely open, this air that is fed back escapes through the valve, with the result that very little if any of this air enters control channel 29d. Consequently, the air flowing through amplifier 29 continues to exit from outlet channel 29b which, in turn, means that the main stream of air flowing through amplifier 28 likewise continues to exit from its outlet channel 28c to plenum 11a. it can thus be seen that so long as valve 31b is entirely open, percent of the conditioned air goes to plenum 11a and 0 percent goes to plenum 12a. Of course, valve 311; does not remain completely open for too long a time under these conditions, but what happens when valve 31b is neither fully closed nor fully open but, rather, somewhere in between, will be taken up later.

Considering now its operation with the bi-metallic strip 31c in its extreme clockwise position, as is illustrated in FIG. 5(b), which means that valve 31a is now fully open and valve 31b completely closed, and assuming again that the conditioned air is initially exiting through outlet channel 28, a small portion of the air flowing through outlet channel 28c is picked up by Pitot tube 30b and, as before, fed back to control channel 29d and valve 31b. In this instance, however, valve 31b is closed, with the result that the air fed back by Pitot tube 30b now enters control channel 29d to cause the stream of air in amplifier 29 to switch from outlet channel 29b to outlet channel 290. When this happens, this second stream of air is directed through control channel 280 into chamber 28f wherein it impinges against the main air stream flowing through amplifier 28 to cause it to switch from outlet channel 280 to outlet channel 28b and from thence to plenum 12a. With the main stream of air now flowing in outlet channel 28b, Pitot tube 30a picks up a small portion of this air and feeds it back to control channel 2% and valve 31a. However, since valve 31a is now completely open, the air fed back to it escapes through it, with the result that very little if any of this air actually enters control channel 2%. Thus, under these conditions, namely, with valve 31b completely closed and valve 31a fully open, 100 percent of the conditioned air goes to plenum 12a and 0 percent goes to plenum 11 a. Here again, of course, valve 31a doesnt remain fully open for very long but, rather, moves toward some condition that is intermediate being fully open or closed.

Thus far, the operation has been described with valves 31a and 31b both closed, with valve 31a fully open and valve 31b closed, and with valve 31a closed and valve 31b fully open, and it was explained that when both valves are closed, the embodiment oscillates with equal pulses of air alternately being directed through outlet channels 28b and 280, that when valve 31b is fully open, the air flows in a DC. (Direct Current) pattern through outlet channel 280, and that when valve 310 is fully open the air flows in a DC. pattern through outlet channel 28b. lt was also explained that the two last mentioned conditions dont remain that way very long and that after a while an intermediate condition is reached as determined by temperature conditions in the room or zone being conditioned.

More particularly, when strip 310 is somewhat left of center, that is to say, has moved somewhat in a counterclockwise direction so that valve 31a is closed and valve 31b is somewhere between being closed and fully open, a constriction exists at valve 31b so that the air fed back to it by Pitot tube 30b cannot escape as easily as it did before when valve 31b was fully open. As a result, some of this air does enter control channel 29d and a back pressure begins to build there, and when this pressure reaches the appropriate level it causes the stream of air in outlet channel 29b to flip or switch to outlet channel 29c which, in turn, causes the main stream of air in outlet channel 28c to flip or switch to outlet channel 28b, as previously described. The abovesaid appropriate pressure level to bring about these changes is determined by the design considerations of the fluidic devices, as will be recognized by those skilled in the art.

With the main air stream now flowing in outlet channel 28b, some air will be fed back by Pitot tube 30a, as already mentioned. However, with valve 310 closed, the air immediately enters control channel 292 and, as previously described in detail, this quickly leads to the main air stream being switched back to outlet channel 28c. Hence, with valve 31a closed and valve 31b being neither closed nor fully open, that is to say, with valve 31b only partially open, once again a pulsed or pulse modulated operation exists but this time, however, the pulses are not of equal duration as they were when both valves were closed. Rather, an oscillation exists in which unequal bursts or pulses of air emanate from outlet channels 28b and 28c, a relatively short pulse out of outlet channel 28b to plenum 12a and a longer pulse out of outlet channel 280 to plenum lla.

Of course, the relative pulse durations at any one time will depend on the position of strip 310 at that time which, in turn, will depend on the temperature conditions in the room or zone to be conditioned at said time. For example, in this kind of situation, the air exiting from outlet channels 28b and 280 may be doing so at an 80 to ratio, 80 percent of the air through outlet channel 28c and 20 percent of the air through outlet channel 28b, or in a 60 to 40 ratio, 60 percent of the air through outlet channel 28c and 40 percent of it through outlet channel 28b, etc., the particular ratio of these pulses of air at any time depending on how nearly the thermostatic conditions of the room or zone to be conditioned are satisfied. Needless to say, the further away they are from being satisfied, the longer the pulses will be through outlet channel 28c, but they become shorter and shorter as the temperature conditions in the room or zone to be conditioned approach the thermostatic setting in that room or zone. At the end, when the temperature conditions in the room or zone are substantially the same as the pre-set thermostatic conditions, the pulses of conditioned air to the two outlet channels and, therefore, to the two plenums, will be of substantially equal duration.

Finally, considering the situation when strip 31c is somewhat to the right of center, that is to say, has

moved somewhat in a clockwise direction so that valve 31b is closed and valve 31a is somewhere between being closed and fully open, a constriction now exists at valve 31a so that the air fed back to it by Pitot tube 30a cannot escape as freely as it did when this valve was fully open. Accordingly, for the same reasons as previously presented in connection with valve 31b, namely, a buildup in pressure to the appropriate level, the air flowing through outlet channel 290 flips to outlet channel 29b and, when this occurs, the air flowing through outlet channel 28b flips to outlet channel 280. At this point, Pitot tube 30b feeds back air to control channel 29d and valve 31b which is closed, with the result that the air flow in outlet channel 29b flips back again to outlet channel 290. correspondingly, the main air flow flips back to outlet channel 28b and the whole above-described cycle starts all over again. Thus, here again, an oscillatory condition exists in which bursts or pulses of air of unequal duration emanate from outlet channels 28b and 28c with the pulses out of outlet channel 280 being of shorter duration than those out of outlet channel 28b. As before, the relative pulse durations will depend on the position of strip 31c at any one time which, it will be remembered, depends on the temperature conditions in the room or zone to be conditioned as compared to the temperature to which thermostat 31 has been set.

It will be recognized from the description presented hereinabove that an induction terminal unit that incor porates a fluidic control system of the kind shown in FIG. 5 is one that is self-regulating in the sense that the operation of the unit will automatically adjust itself to maintain the ambient temperature, that is to say, the temperature of the room or zone, as nearly equal as possible to the temperature at which the thermovalve is set. More particularly, as was previously explained, equal pulses of air are directed to plenums 11a and 12a when the ambient temperature is the same as the temperature setting of the thermovalve. if this condition or state of operation is adequate to keep the ambient temperature at the temperature setting of the thermovalve, then the air out of the fluidic control system will continue to be divided equally between the plenums. However, as is usually the case, the ambient temperature will begin to shift after awhile, and when this occurs the unit will automatically compensate for this shift by increasing the duration of the pulses to one plenum or the other to bring the ambient temperature back to the temperature setting of the thermovalve. For example, if the ambient tamperature should rise above the temperature setting of the thermovalve, then in that event the duration of the pulses of cold air to plenum 1 la will correspondingly increase and the ambient temperature will begin to decline. On the other hand, if the ambient temperature should fall below the temperature setting of the thermovalve, then in that event the duration of the pulses of cold air to plenum 11a will correspondingly decrease and the ambient temperature will then ultimately rise. Thus, an induction terminal unit of this kind is one that constantly seeks to maintain an equality between the ambient tamperature and the temperature setting of the thermovalve.

Another embodiment of an induction terminal unit according to the present invention, involving the use of twin coils for heating and cooling purposes and a tristable fluidic amplifier as the fluidic control system, is illustrated in FIG. 6. More particularly, this embodiment includes a first bank of three plenums 32, 33 and 34 and a second bank of three plenums 35, 36 and 37 mounted above the first bank of plenums and respectively coupled to them by means of three sets of air tubes 38, 39 and 40. Plenums 32-34 are the same as those previously identified as plenums 11a and 12a, and except, perhaps, for differences in length, the same may be said as to air tubes 38-40, namely, that air tubes 38-40 are like air tubes 11c and 120. As for plenums 35-37, they very closely resemble plenums 11b and 12b described earlier but there are some differences that makes some further description of plenums 35-37 worthwhile.

More particularly, plenums 35 and 36 are substantially identical with plenums 11b and 12b, as can be seen from a comparison of FlGS. 3 and 6. Thus, plenums 35 and 36 respectively include top walls 35a and 36a that are made of some sort of screen, mesh or grill arrangement that permits air to flow from these plenums into the room or zone in which the unit is located. Similarly, plenums 35 and 36 also include outside walls 35b and 36b made of the same kind of screen, mesh or grill arrangement so as to permit ambient air to enter these plenums. Finally, as in plenum 11b, plenum 35 has a coil 41 mounted in it just inside wall 35b so that any ambient air entering the plenum through said wall will come into contact with the coil. Although coil 41 may be-either a cooling or heating coil, it will be considered to be a cooling coil throughout the description that follows. As can be seen from FIG. 6, plenums 35 and 36 are respectively interconnected or intercoupled with plenums 32 and 33 by air tubes 38 and 39.

Considering now plenum 37, this plenum has the same generally L-shaped configuration as plenum 36 and is interconnected or intercoupled with plenum 34 by means of air tubes 40. The top and side walls of plenum 37, also made of suitable screen, mesh or grill materials of some sort, are respectively designated 37a and 37b and, as can be seen from the drawing, top walls 35a-37a, together with the elements that separate and support them, actually form the top wall of the terminal unit as a whole. Similarly, side walls 35b-37b, together with the elements that separate and support them, form a major portion of the wall of the unit facing the room or zone. Finally, plenum 37 also has a heating coil 42 mounted within it that is spaced to some extent from the wall that is common between plenums 36 and 37, namely, wall 370, the reason being so that ambient air entering plenum 37 will have ample space to flow easily between wall 37c and coil 42. To force the entering ambient air to do just that, namely, flow into the space between wall 370 and coil 42, plenum 37 also includes a baffle 37d mounted between plenum 34 and coil 42 that blocks off the rest of the plenum from this ambient air. Thus, in a sense, baffle 37d and coil 42 together form a wall that divides plenum 37 into two chambers 37f and 37e that are coupled to each other through coil 42.

From the description, it can be seen that plenums 35 and 37 are coil plenums whereas plenum 36 is a bypass plenum. It will also be recognized that plenums 35 and 36 are utilized when the room or zone is to be cooled, and that plenums 37 and 36 are utilized when the room or zone is to be warmed or heated. Thus, whereas the terminal unit in FIGS. 2 and 3 employs a single coil plenum'and, therefore, a single coil for both heating and cooling by selectively circulating hot or cold water through it, the FIG. 6 unit utilizes two coil plenums and, therefore, two coils for the same purposes, one plenum and coil being used only for cooling purposes and the other plenum and coil being used only for heating purposes.

Considering now its operation, it will first be assumed that the room or zone in which the unit is located will be cooled when air-conditioning is required, as may be the case, for example, during the summer months. Accordingly, cold water is circulated in coil 41 and the pre-conditioned air that is delivered to either of plenums 32 or 33 is cold air. Under these first-assumed conditions, plenums 34 and 37 are therefore not in use at all and, to avoid waste, no hot water is being circulated through coil 42. The portion of the FIG. 6 embodiment that is in operation, therefore, is the same as the structure shown in FIGS. 2 and 3, and the operation is the same too. Accordingly, briefly stated, pre-conditioned air entering plenum 32 passes via air tubes 38 into plenum 35 where the aforementioned low-pressure region is developed that attracts ambient air to it. This ambient air is cooled by coil 41, the resulting mixture of pre-conditioned and cooled ambient air then flowing into the room or zone to cool it. When the room or zone is not to be conditioned, the pre-conditioned air flows into plenum 33 instead and from there into plenum 36 through which the ambient air is bypassed.

Assuming now that the room or zone in which the unit is located is to be heated when air-conditioning is required, as may be the case during the winter months, hot water is now circulated in coil 42 and the preconditioned air that is delivered to either of plenums 33 and 34 is now hot air. In this instance, plenums 32 and 35 are the ones not in operation and, therefore, may be ignored, and no cold water is being circulated in coil 41. Assuming now that the pre-conditioned air is directed into plenum 34, this pre-conditioned air passes through air tubes 40 and into chamber 37e of plenum 37. As a result, a low-pressure region is developed in chamber 37e that immediately spreads to chamber 37d and the rest of plenum 37. Ambient air is thereby sucked or induced into plenum 37 through wall 37b. This ambient air is directed by baffle 37d into chamber 37d where it is then brought into contact with coil 42 as it passes into chamber 37e to mix with the preconditioned air already therein. The mixture of hot preconditioned and ambient air then passes through wall 37a and into the room or zone to heat it. When conditioning is no longer required, the pre-conditioned air is directed to plenum 33 and, as previously explained, the ambient air then flows instead through plenum 36 to thereby bypass the coil. Since the ambient air is now not being heated and since the ambient air constitutes a major portion of the air passing into the room or zone, the room or zone is now no longer being conditioned to any significant extent.

Since the FIG. 6 terminal unit has three inputs to it, namely, plenums 32-34, a tri-stable fluidic amplifier 43 is used in the fluidic control system rather than the bistable amplifier previously described. More specifically, in addition to an inlet channel 43a that is coupled to supply duct 22 and a pair of control channels 43b and 43c that are coupled to a thermovalve 44, the tri-stable amplifier also includes three outlet channels 43d, 43e and 43]" that respectively couple and feed into plenums 32, 33 and 34. As can be seen from the figure, thermovalve 44 basically includes a coiled bi-metallic strip 44a and a pair of air valves, generally designated 44b and 44c, that are respectively coupled to control channel 43b and 43c by means of a pair of tubes or hoses 45a and 45b. Thermovalve 44 is of the kind where either one or the other of air valves 44b and 44c are open, or both are open, at any one time.

Considering now the operation of the fluidic control system in FIG. 6, it will be recognized by those skilled in the fluidic amplifier art that when valve 44b is open and valve 440 closed, which means that control channel 43b is open and control channel 43c is closed, the preconditioned air flowing through fluidic amplifier 43 is directed to outlet channel 43d and, therefore, to plenum 32. This, it will be remembered, is the condition that exists when the pre-conditioned air is cold air and when the room or zone in which the induction terminal unitis located needs to be cooled. Of course, the fluidic control system determines that the room or zone needs to be cooled and directs cold air to plenum 32 in the manner just described when the temperature at which thermovalve 44 is set is lower than the ambient temperature of the room or zone. On the other hand, when the temperature at which the thermovalve is set is higher than the ambient temperature of the room or zone, then valve 44b is closed and valve 44c opens which, in turn, means that control channel 43b is closed and control channel 430 open. The result of the thermovalve and the control channels being in this state is that the pre-conditioned air flowing through fluidic amplifier 43 is now directed to outlet channel 43f and from there to plenum 34, which, it will again be remembered, is the situation when the pre-conditioned air is hot air and the room or zone in which the unit is located needs-to be warmed. Finally, valves 44b and 440 are both open and, therefore, control channels 43b and 43c are both open, when the temperature at which thermovalve 44 is set is substantially the same as the ambient temperature. Under such circumstances, in accordance with the well known principles governing the operation of tri-stable amplifier devices, the stream of pre-conditioned air flowing through the amplifier, whether it be hot or cold air, is directed to outlet channel 43e and, therefore, to plenum 33. When the preconditioned air flows to plenum 33, it will be remembered, the ambient air takes the bypass path through plenum 36 and, therefore, is neither cooled nor heated by the coils, which is exactly what is to be expected when the room or zone needs neither to be cooled nor heated.

Although a number of embodiments of an induction terminal unit according to the present invention have been illustrated and described hereinabove, it is to be understood that the invention is not entirely confined or limited thereto but, rather, should be considered to include any and all modifications, alterations or equivalent arrangements falling within the scope of the invention.

For example, referring to the fluidic control system of FIG. 4, a monostable fluidic amplifier could be substituted for the bistable amplifier shown there, a monostable amplifier being one that is biased so that the flow through the device is always through the same outlet channel unless something is done to switch the flow to the other one. Monostable fluidic amplifier devices are very well known in the art. Since the schematic for a monostable amplifier is the same as that for a bistable one, it was not deemed necessary to provide a separate figure to show such a modification to the fluidic control system. Thus, assuming that amplifier 25 is now of the monostable type and assuming also that it is biased so that the pre-conditioned air normally flows to outlet channel 25b and, therefore, to plenum 12a, the flow will be switched to outlet channel 25c and, therefore, to plenum 11a when solenoid 27b is activated and it will continue to flow in this direction so long as the solenoid remains activated. Needless to say, because of the built-in bias of the device, the flow will automatically switch back to outlet channel 25b as soon as the solenoid is deactivated. Actually, therefore, solenoid 27a is not needed in this kind of a situation and can be removed from the system.

Another modification is'possible in connection with the fluidic control system shown in FIG. 5. More specifically, the system shown there works on the basis of positive pressures fed back by Pitot tubes 30a and 30b. However, this system can work just as well on the basis of negative pressures and this can be done simply by reversing the directions of the Pitot tubes and the connections between control channels 29d and 29e with air valves 31a and 31b. Thus, by reversing the direction of Pitot tubes 30a and 30b so that they point downstream instead, thereby causing negative pressures (partial vacuums) to be fed back to the air valves, and by connecting valve 31a to control channel 29d and valve 31b to control channel 29e, th'e fluidic control system will act in the same described manner.

The above are only a couple of modifications. Many others are possible. Accordingly, the invention is to be considered limited only by the scope of the annexed claims.

Having thus described the invention, what is claimed 1. In an air-conditioning system in which preconditioned air is ducted to each of a plurality of rooms, an induction terminal system for each of said rooms that comprises: a terminal unit having at least coil and bypass plenums through which a mixture of the pre-conditioned and room air selectively flows, said coil plenum including first and second air inlet means to respectively permit entry of said pre-conditioned and room air thereto, room air being induced to enter and flow through said coil plenum only when preconditioned air flows therethrough, first air outlet means to permit said mixture of pre-conditioned and room air to discharge directly into the room, and a coil for conditioning room air mounted in said second air inlet means, said bypass plenum including third and fourth air inlet means to respectively permit entry of said pre-conditioned and room air thereto, room air being induced to enter and flow through said bypass plenum only when pre-conditioned air flows therethrough, and second air outlet means to permit said mixture of pre-conditioned and room air to discharge directly into the room, said coil and bypass plenums including additional means to isolate one plenum from the other in such a manner that air flowing in one will not mix with and will not affect air in the other prior to discharge into the room; and a fluidic control unit for switching the entire stream of pre-conditioned air to a selected one of said plenums in response to air-pressure cludes at least an inlet channel into which the preconditioned air stream flows, first and second outlet channel's respectively coupled to said coil and bypass plenums and to which the stream of pre-conditioned air flows, and a pair of control channels through which airpressure signals are selectively directed against said pre-conditioned air stream to switch its flow from one of said outlet channels to the other, said fluidic control unit further including air-pressure means coupled to said pair of control channels and operable in response to an appropriate signal to cause an air-pressure signal to be applied thereto to switch the flow of said preconditioned air stream, and thermostatic apparatus to apply said appropriate signal to said air-pressure means when the temperature in the room reaches a predetermined level.

2. The induction terminal system defined in claim 1 wherein said coil plenum includes separate and distinct first and second plenums, said first plenum including said first air inlet means and said second plenum including said second air inlet means, said first air outlet means, and said coil, said coil plenum further including coupling means that provides a path that permits conditioned air entering said first plenum to flow into said second plenum.

3. The induction terminal system defined in claim 1 wherein said bypass plenum includes separate and distinct third and fourth plenums, said third plenum including said third air inlet means and said fourth plenum including said fourth air inlet means and said second air outlet means, said bypass plenum further including coupling means that provides a path that permits conditioned air entering said third plenum to flow into said fourth plenum.

4. The induction terminal system defined in claim 1 wherein said coil plenum includes separate and distinct first and second plenums, said first plenum including said first air inlet means and said second plenum including said second air inlet means, said first air outlet means, and said coil, said coil plenum further including coupling means that provides a path that permits conditioned air entering said first plenum to flow into said second plenum; and wherein said bypass plenum includes separate and distinct third and fourth plenums, said thirdplenum including said third air inlet means and said fourth plenum including said fourth air inlet means and said second air outlet means, said bypass plenum further including coupling means that provides a path that permits conditioned air entering said third plenum to flow into said fourth plenum.

5. The induction terminal system defined in claim 2 wherein said coupling means includes a set of tubes that intercouple said first and second plenums and through which the conditioned air flows therebetween.

6. The induction terminal system defined in claim 3 wherein said coupling means includes a set of tubes that intercouple said third and fourth plenums and through which the conditioned air flows therebetween.

7. The induction terminal system defined in claim 4 wherein the coupling means in said coil plenum includes a first set of tubes that intercouple said first and second plenums and through which the conditioned air flows therebetween, and wherein the coupling means in said bypass plenum includes a second set of tubes that intercouple said third and fourth plenums and through which the conditioned air flows therebetween.

8. The induction terminal system defined in claim 4 wherein said first and third plenums are ducts that are closed at one end and open at the other end, said open ends being coupled to receive the conditioned air, and wherein the coupling means in said coil and bypass plenums respectively include first and second sets of tubes that respectively extend from said first and third plenums into said second and fourth plenums to provide a path therebetween for the conditioned air.

9. The induction terminal system defined in claim 1 wherein said fluidic amplifier arrangement includes a monostable fluidic amplifier device that is biased in its construction so that the pre-conditioned air stream flowing therethrough normally flows to one of said plenums, said monostable amplifier device being operable in response to said pressure signals to switch the flow of said stream to the other of said plenums.

10. The induction terminal system defined in claim 1 wherein said fluidic amplifier arrangement includes a bistable fluidic amplifier device, the outlet channel thereof through which said air stream flows being selected under the control of said thermostatic apparatus.

11. The induction terminal system defined in claim 1 wherein said terminal unit further includes a second coil plenum through which a mixture of the preconditioned and room air selectively flows, said second coil plenum including fifth and sixth air inlet means to respectively permit entry of said pre-conditioned and room air thereto, room air being induced to enter and flow through said second coil plenum only when preconditioned air flows therethrough, third air outlet means to permit said mixture of pre-conditioned and room air to discharge directly into the room, and a second coil for conditioning room air mounted in said sixth air inlet means.

12. The induction terminal system defined in claim 4 wherein said terminal unit further includes a second coil plenum having separate and distinct fifth and sixth plenums, said fifth plenum including fifth air inlet means to permit entry of pre-conditioned air thereto and said sixth plenum including sixth air inlet means to permit entry of room air thereto, third air outlet means, and a second coil for conditioning room air, said second coil plenum further including coupling means that provides a path that permits conditioned air entering said fifth plenum to flow into said sixth plenum.

13. The induction terminal system defined in claim 8 wherein said terminal unit further includes a second coil plenum having separate and distinct fifth and sixth plenums, said fifth plenum including fifth air inlet means to permit entry of pre-conditioned air thereto and said sixth plenum including sixth air inlet means to permit entry of room air thereto, third air outlet means, and a second coil for conditioning room air, said fifth plenum being a duct that is closed at one end and open at the other end to receive the pre-conditioned air, and wherein said second coil plenum includes a third set of tubes that extend from said fifth plenum into said sixth plenum to provide a path therebetween for the preconditioned air.

14. The induction terminal system defined in claim 13 wherein said fluidic amplifier arrangement includes a tri-stable fluidic amplifier device mounted between said first, third and fifth plenums on the one hand and the duct by means of which the pre-conditioned air is conveyed to the induction terminal system on the other hand, said device being operable in response to said airpressure signals to switch the entire flow of preconditioned air from one to another of said first, third and fifth plenums. 

1. In an air-conditioning system in which pre-conditioned air is ducted to each of a plurality of rooms, an induction terminal system for each of said rooms that comprises: a terminal unit having at least coil and bypass plenums through which a mixture of the pre-conditioned and room air selectively flows, said coil plenum including first and second air inlet means to respectively permit entry of said pre-conditioned and room air thereto, room air being induced to enter and flow through said coil plenum only when pre-conditioned air flows therethrough, first air outlet means to permit said mixture of pre-conditioned and room air to discharge directly into the room, and a coil for conditioning room air mounted in said second air inlet means, said bypass plenum including third and fourth air inlet means to respectively permit entry of said pre-conditioned and room air thereto, room air being induced to enter and flow through said bypass plenum only when pre-conditioned air flows therethrough, and second air outlet means to permit said mixture of pre-conditioned and room air to discharge directly into the room, said coil and bypass plenums including additional means to isolate one plenum from the other in such a manner that air flowing in one will not mix with and will not affect air in the other prior to discharge into the room; and a fluidic control unit for switching the entire stream of pre-conditioned air to a selected one of said plenums in response to air-pressure signals, said fluidic control unit including a fluidic amplifier arrangement that has no moving parts for switching the stream of pre-conditioned air and that itself includes at least an inlet channel into which the preconditioned air stream flows, first and second outlet channels respectively coupled to said coil and bypass plenums and to which the stream of pre-conditioned air flows, and a pair of control channels through which air-pressure signals are selectively directed against said pre-conditioned air stream to switch its flow from one of said outlet channels to the other, said fluidic control unit further including air-pressure means coupled to said pair of control channels and operable in response to an appropriate signal to cause an air-pressure signal to be applied thereto to switch the flow of said pre-conditioned air stream, and thermostatic apparatus to apply said appropriate signal to said air-pressure means when the temperature in the room reaches a pre-determined level.
 2. The induction terminal system defined in claim 1 wherein said coil plenum includes separate and distinct first and second plenums, said first plenum including said first air inlet means and said second plenum including said second air inlet means, said first air outlet means, and said coil, said coil plenum further including coupling means that provides a path that permits conditioned air entering said first plenum to flow into said second plenum.
 3. The induction terminal system defined in claim 1 wherein said bypass plenum includes separate and distinct third and fourth plenums, said third plenum including said third air inlet means and said fourth plenum including said fourth air inlet means and said second air outlet means, said bypass plenum further including coupling means that provides a path that permits conditioned air entering said third plenum to flow into said fourth plenum.
 4. The induction terminal system defined in claim 1 wherein said coil plenum includes separate and distinct first and second plenums, said first plenum including said first air inlet means and said second plenum including said second air inlet means, said first air outlet means, and said coil, said coil plenum further including coupling means that provides a path that permits conditioned air entering said first plenum to flow into said second plenum; and wherein said bypass plenum includes separate and distinct third and fourth plenums, said third plenum including said third air inlet means and said fourth plenum including said fourth air inlet means and said second air outlet means, said bypass plenum further including coupling means that provides a path that permits conditioned air entering said third plenum to flow into said fourth plenum.
 5. The induction terminal system defined in claim 2 wherein said coupling means includes a set of tubes that intercouple said first and second plenums and through which the conditioned air flows therebetween.
 6. The induction terminal system defined in claim 3 wherein said coupling means includes a set of tubes that intercouple said third and fourth plenums and through which the conditioned air flows therebetween.
 7. The induction terminal system defined in claim 4 wherein the coupling means in said coil plenum includes a first set of tubes that intercouple said first and second plenums and through which the conditioned air flows therebetween, and wherein the coupling means in said bypass plenum includes a second set of tubes that intercouple said third and fourth plenums and through which the conditioned air flows therebetween.
 8. The induction terminal system defined in claim 4 wherein said first and third plenums are ducts that are closed at one end and open at the other end, said open ends being coupled to receive the conditioned air, and wherein the coupling means in said coil and bypass plenums respectively include first and second sets of tubes that respectively extend from said first and third plenums into said second and fourth plenums to provide a path therebetween for the conditioned air.
 9. The induction terminal system defined in claim 1 wherein said fluidic amplifier arrangement includes a monostable fluidic amplifier device that is biased in its construction so that the pre-conditioned air stream flowing therethrough normally flows to one of said plenums, said monostable amplifier device being operable in response to said pressure signals to switch the flow of said stream to the other of said plenums.
 10. The induction terminal system defined in claim 1 wherein said fluidic amplifier arrangement includes a bistable fluidic amplifier device, the outlet channel thereof through which said air stream flows being selected under the control of said thermostatic apparatus.
 11. The induction terminal system defined in claim 1 wherein said terminal unit further includes a second coil plenum through which a mixture of the pre-conditioned and room air selectively flows, said second coil plenum including fifth and sixth air inlet means to respectively permit entry of said pre-conditioned and room air thereto, room air being induced to enter and flow through said second coil plenum only when pre-conditioned air flows therethrough, third air outlet means to permit said mixture of pre-conditioned and room air to discharge directly into the room, and a second coil for conditioning room air mounted in said sixth air inlet means.
 12. The induction terminal system defined in claim 4 wherein said terminal unit further includes a second coil plenum having separate and distinct fifth and sixth plenums, said fifth plenum including fifth air inlet means to permit entry of pre-conditioned air thereto and said sixth plenum including sixth air inlet means to permit entry of room air thereto, third air outlet means, and a second coil for conditioning room air, said second coil plenum further including coupling means that provides a path that permits conditioned air entering said fifth plenum to flow into said sixth plenum.
 13. The induction terminal system defined in claim 8 wherein said terminal unit further includes a second coil plenum having separate and distinct fifth and sixth plenums, said fifth plenum including fifth air inlet means to permit entry of pre-conditioned air thereto and said sixth plenum including sixth air inlet means to permit entry of room air thereto, third air outlet means, and a second coil for conditioning room air, said fifth plenum being a duct that is closed at one end and open at the other end to receive the pre-conditioned air, and wherein said second coil plenum includes a third set of tubes that extend from said fifth plenum into said sixth plenum to provide a path therebetween for the pre-conditioned air.
 14. The induction terminal system defined in claim 13 wherein said fluidic amplifier arrangement includes a tri-stable fluidic amplifier device mounted between said first, third and fifth plenums on the one hand and the duct by means of which the pre-conditioned air is conveyed to the induction terminal system on the other hand, said device being operable in response to said air-pressure signals to switch the entire flow of preconditioned air from one to another of said first, third and fifth plenums. 